The membrane properties which control Ca2 ion uptake and binding by sarcoplasmic reticulum Ca2 ion ATPase are investigated in a reconstituted vesicular system. The local phospholipid environment of the enzyme including the identity of the bound phospholipids and the nature of the binding interactions are examined using nuclear magnetic resonance (NMR) spectroscopy and fluorescence spectroscopy. These physical parameters will be correlated with Ca2 ion transport and ATPase activity. It will then be possible to examine how the enzyme activity and membrane physical parameters can be influenced by factors such as cation concentration and pH which have been implicated in pathological cardiac conditions.